Molded article of metal matrix composite and method for making such an article

摘要

A molded brake disc having a central hub portion and an annular disc portion extending from the hub portion in a radial outward direction for frictional engagement with brake pads, wherein the disc portion is formed of metal matrix composite having a reinforcing material added to a metal matrix, and the hub portion is formed of metal which is inexpensive as compared to the metal matrix composition. Due to a limited use of the expensive metal matrix composite, the molded brake disc as a whole is inexpensive as compared to a conventional molded brake disc entirely formed of metal matrix composite. Such molded brake disc can readily be formed by an improved injection molding method, wherein a metal matrix composite material in a molten state and a metallic material in a semi-solidified state are supplied into an injection cylinder such that the metal matrix composite material is situated on a gate side adjacent to a gate of a molding die and the metallic material is situated on a piston side adjacent to a piston in the injection cylinder, and the metal matrix composite material and the metallic material are then forced by the piston into a die cavity in the molding die in the order named.